Gas sampling device

ABSTRACT

A gas sampling device has a gas-entry passage dimensioned to provide laminar flow to the gas and opening into a larger gas-receiving passage. A gas sampling tube is supported from the larger gas-receiving passage, extends only to the smaller gas-entry passage for sampling the entering gas, and is coaxially spaced from the walls of the gas-entry passage to sample the gas in the gas-entry passage without dilution from the gas-receiving passage or interference with the gas flow. The device is particularly useful for sampling small exhaled breath gas flow in combination with neonatal respiratory apparatus for sampling the breath of neonates.

BACKGROUND OF THE INVENTION

The invention relates to a device for sampling a flowing gas.

Many medical and industrial activities require samples of flowing gasesfor analysis and control of the activity. When the flow of such gases isvery small, however, it has been difficult to provide a device whichsamples the gases accurately and without undesirably interfering withthe limited flow of the gas.

In medical activities such as the administration of ventilation oranesthesia gases to patients with an endotracheal tube, for example, thegas exhaled by the patient can be sampled and analyzed for diagnosis orcontrol of the apparatus. With adult patients, the endotracheal tube islarge enough to accomodate a coaxial sampling tube, but with infants orneonates, the endotracheal tube is too small for such an arrangement. Inaddition, the flow of gas from the neonate is so small that the gassampling apparatus can easily interfere with the flow of gas.

Typically, the necessarily small endotracheal tube for use on a neonateis connected to larger tubing more practical for administering therespiratory or anesthesia gases in a valve arrangement which also ventsthe gases exhaled by the neonate. Because the flow of exhaled gas issmall and the valve arrangement is of relatively substantial volume tobe of a practical size, the exhaled gases mix with gases supplied forthe previous inhalation cycle in the valve arrangement. Sampling theexhaled gas after it leaves the endotracheal tube thus provides aninaccurate sample. It has therefore been the practice to try to positiona flexible gas-sampling tube as close to the connection to theendotracheal tube as possible. The flexible tube, however, had to beabout the same size as the neonatal endotracheal tube to bepositionable, and thus could substantially block the endotracheal tubeif it got too close. The resulting compromise in positioning theflexible tube near enough the endotracheal tube for an accurate samplebut not blocking it, and the difficulty of achieving even thiscompromise, made the arrangement impractical.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a device forsampling a flowing gas, and particularly a device for accuratelysampling small gas flows.

To this end, the invention provides a device having a gas-entry passagedimensioned in accordance with the gas flow for providing substantiallylaminar flow to the gas. The gas-entry passage opens into a largergas-receiving passage of, for example, a size for more convenienthandling. A rigid gas sampling tube is supported from the largergas-receiving passage, projects only to the gas-entry passage, and isspaced coaxially from the walls thereof for sampling the laminar flow ofthe gas in the gas entry passage without interfering with the flow ofthe gas to be sampled even when the gas flow is very small. In addition,the laminar flow of the gas in the gas entry passage prevents mixture ofthe gas flow to be sampled with gases which may remain in the largergas-receiving passage, particularly in the center of the laminar gasflow. Positioning the sampling tube coaxially of the gas-entry passagethus provides the most accurate sample of the flowing gas. A stillfurther advantage of the spaced, coaxial position of the gas samplingtube is that condensation or other fluids from the walls of thegas-entry passage cannot flow into the sampling tube to block the tubeor interfere with instruments for analyzing the sampled gas.

Each of these advantages of the invention is especially important whenthe flow of gas to be sampled is very small and moist as with theexhalation gas of a neonate through an endotracheal tube which isconnected to a respiratory device such as a ventilator or anesthesiadevice by the sampling device. In this arrangement, the gas-entrypassage which is small enough relative even to the limited exhalationbreath gas flow to make the exhaled gases flow laminarly restricts theback-flow or dilution of the exhaled breath gas to be sampled withrespiration or anesthesia gases remaining in the enlarged gas-receivingportion from the preceding inhalation cycle. Sampling the exhaled breathgas at the gas entry passage, and particularly at the center thereof,thus provides the most accurate breath sample. Positioning the samplingtube at and in the center of the gas-entry passage where it enlargesinto the gas-receiving passage also avoids flow interference. Supportingthe sample tube only in the larger gas receiving passage still furtheravoids flow interference. The arrangement also can be made in just twomating parts, one for connection to the endotracheal tube and one forconnection to the respirator or anesthesia device. The samplingarrangement then also provides a convenient adapter for the differingpassage dimensions of the endotracheal tube and respiratory devicehaving a minimum of dead space which can interfere with regulating therespirator or anesthesia device.

DESCRIPTION OF THE DRAWINGS

A preferred embodiment which illustrates but does not limit theinvention will now be described with reference to the FIGURE which is anenlarged elevation, partly in section, of the preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment is a device for sampling the exhaled breath gasof a neonate. The breath gas is supplied through an endotracheal tubehaving a proximal end at 10 in which a gas entry passage 12 of thedevice is received. At the opposite end of the device is a gas supplyvalve arrangement 14 of a ventilator. During inhalation, gas flows fromthe ventilator valve at 14 to the gas-entry passage 12 and endotrachealtube at 10 and during exhalation, gas flows in the opposite directionfrom the endotracheal tube at 10 and the gas-entry passage 12 to theventilator valve at 14. During exhalation, with the expired breath gasflowing into the gas entry passage 12 from the endotracheal tube at 10,or to the right in the Figure, the expired breath gas is sampled with agas sample tube 16.

The gas sample tube is an L-shaped, rigid pipe extending from asupporting connection in one member 18 of the device to the gas-entrypassage 12 which is in another member 20 of the device. The two members18, 20 mate in gas-tight sliding engagement so that they may beseparated as desired for easier connection of the endotracheal tube tothe gas entry passage, or for other reasons. The end of the member 18opposite that which mates with the gas-entry passage member 20 mateswith the ventilator valve 14 and thus has the convenient, approximatelyone half inch (1.2 cm) flow line dimensions of such equipment anddefines a larger gas-receiving passage 22 in the two mating members 18,20.

The larger dimensions of the gas-receiving passage 22 are too big tomaintain laminar flow of the limited breath exhalation gas flow from aneonate. The gas-entry passage 12, however, is dimensioned relative tothe exhalation flow to establish or maintain laminar flow of theexhalation gas in the gas-entry passage. The sample tube 16 extends justto the proximal end of the gas-entry passage 12 where it opens into thegas-receiving passage 22, as shown in the Figure, to sample the laminarflow of the exhaled breath gas. The sample tube 16 is also positioned byits support on the member 18 and the mated position of the member 20therein to be coaxially spaced from the walls of the gas entry passage.This structural arrangement provides the several gas-samplingimprovements of the invention.

By positioning the gas-sampling tube where the gas-entry opens into thelarger gas-receiving passage even a slight spacing of the tube from thewalls of the gas-entry passage is sufficient to keep the tube fromsubstantially limiting the gas flow. This is particularly important whenthe gas flow is small, because the gas-entry passage is thencorrespondingly small to provide the laminar flow for better samplingand the sample tube size required to obtain a sample may be so close tothat of the gas entry passage as to restrict the gas flow if the sampletube projected further into the gas-entry passage. Supporting thegas-sampling tube from the larger gas receiving passage further avoidsrestricting the gas flow with the support, and also avoids interferencewith the laminar flow.

Providing the laminar flow in the gas-entry passage where the gas issampled is important to avoid dilution of the gas to be sampled withother gases. Turbulent flow would tend to mix in some other gases fromthe gas-receiving passage, such as anesthesia gases from the preceedinginhalation breath cycle when the valve 14 connects to an anesthesiadevice, and thus provide an inaccurate sample of the exhaled gas.Positioning the gas-sampling tube centrally of the gas-entry passagealso samples the central, maximum gas flow to aid the anti-dilutioneffect and avoids picking up moisture from the walls of the gasreceiving passage. The anti-dilution effect is also heightened byproviding progressively diverging walls 24 connecting the gas-entrypassage 12 to the gas-receiving passage 22 to help direct a flow of gasaway from the gas sample tube.

The exterior portion 26 at the diverging junction of the gas-entrypassage with the larger gas-receiving passage provides a flange whichlocates the proximal end of the endotracheal tube 10 on the exterior ofthe gas-receiving passage. Predictably locating the gas-sampling tube inrelation to the endotracheal tube in this way further assists inaccurately sampling the gas.

The gas-receiving passage 22 is preferably only about 3/4inch (1.9 cm)long to minimize the dead space which is added to the ventilator oranesthesia system by the sampling device. Such dead-space with thepressure-elasticity of gases can interfere or at least alter theperformance of the ventilator or anesthesia devices if it is excessive.The small size of the gas sampling device minimizes such effects.

Having thus described my invention,

I claim:
 1. A device for sampling a flowing gas comprising:gas-entrymeans defining a passage for receiving the flowing gas and providingsubstantially laminar flow to the gas to an exit end; gas-receivingmeans of larger capacity than the passage of the gas-entry means andconnected to the exit end of the gas-entry means for receiving theflowing gas from the exit end of the gas-entry means without substantialreturn dilution thereto; and a gas-sampling tube supported only at oneend from the gas-receiving means for not impairing the laminar flow inthe gas entry means and projecting at the other end only to the exit endof the gas-entry means and coaxially spaced from the passage therein forsampling the flowing gas, the gas-sampling tube projecting through thegas receiving means for connection to a device processing the sampledgas.
 2. A device for sampling a flowing gas comprising:a first memberhaving a gas-entry passage at one end of sufficiently small diameterrelative to the gas flow to establish substantially laminar flow of thegas therein and opening into a gas-receiving passage of larger diameterat the other end; and a second member having a sleeve and gas-samplingtube, the sleeve being of a diameter for mating with the gas-receivingpassage, and supporting the gas-sampling tube which extends out of thesleeve for connection to a gas processing device at one end, and only toand coaxially spaced from the gas-receiving passage at the other endwhen the members are mated.
 3. The device of claim 1 or 2 and furthercomprising, in combination, a respiratory device connected to thegas-receiving passage for supplying a second gas and an endotrachealtube connected to the gas-entry passage for carrying the second gas to apatient during inhalation and providing the flowing gas to be sampledduring exhalation.
 4. The device of claim 3 and further comprising meanson the gas-entry passage for locating the proximal end of theendotracheal tube at the end of the gas-sampling tube in thegas-receiving passage.
 5. The device of claim 1 or 2 and furthercomprising progressively diverging walls connecting the gas-entrypassage to the gas-receiving passage.